考虑可压缩性的高水头水泵水轮机空化与振动问题研究

Cavitation and vibration problem are important factors restricting the development of high-head pump turbine. In order to solve this problem, a state equation of mixture fluid is established based on a barotropic state law, combining with the homogeneous equilibrium modeling approach, a cavitation model considering the compressibility of water is obtained. A pump turbine model testbed is built to conduct cavitation and vibration test, and the cavitation model considering the compressibility of water is verified by model test. Considering the compressibility of water, numerical simulations of pump turbines with different head from 200m to 800m are carried out, and the applicable head range of the water compressibility in numerical simulation and the effect on the performance prediction are exploratory researched. The flow characteristics of high-head pump turbine at different operating condition are simulated by using compressible flow cavitation model, and the nature reasons of unstable problems in pump turbine are reveled, the unstable problems include “S” characteristics, rotor and stator interaction, rotating stall, and hump characteristics. To achieve independently design of high-head pump turbine, the effect of runner geometry parameters on the cavitation performance and vibration characteristic is investigated, and the solution method of compressible fluid cavitation problem combines with the optimization strategy of hydraulic efficiency, to achieve the multiple target optimization design of high-head pump turbine.

空化与振动问题是制约我国高水头水泵水轮机发展的重要因素。针对这一问题，基于正压规律构建混合流体的状态方程，结合均质平衡流模型，建立考虑流体可压缩性的空化模型。并在水泵水轮机模型试验台进行空化与振动试验研究，对考虑可压缩流动的空化模型进行试验验证。在此基础上考虑不同水头段的水的可压缩性模型，用于中高水头乃至800米以上水泵水轮机精确数值模拟，探索性研究混合流体的不同参数对高水头水泵水轮机性能的影响及其流动特性的影响,以此获得可压缩流动的空化模型在不同水头段的运行规律及其适用范围，从而揭示高水头水泵水轮机不同工况下的流动特征，阐明“S”特性、旋转失速、动静干涉及驼峰区不稳定等水泵水轮机中常见问题的根本原因。并将可压缩流动的空化问题求解与转轮水力效率优化策略相结合，寻求高水头水泵水轮机转轮能量与空化性能多重目标的优化设计方法，以达到实现高水头水泵水轮机具有自主产权的设计理念。

空化与振动问题是制约我国高水头水泵水轮机发展的两个重要因素。本项目基于正压规律构建混合流体的状态方程，结合均质平衡流模型，建立了考虑流体可压缩性的空化模型，在此基础上，通过数值模拟与实验相结合的方法，分析了流体可压缩性对水泵水轮机“S”特性和驼峰特性的影响，结果表明考虑可压缩性得出的特性曲线的误差较小，并且能够捕捉到更丰富的压力脉动特性；通过对比分析不同工况下的流动特征，揭示了水流阻滞的形成机理、产生的工况条件以及引起的压力场变化规律，探讨了水轮机工况转轮不同叶片间的水流阻滞现象和水泵工况挡水环现象及其引起的压力脉动的频率特性，阐明了水轮机70%以下出力工况振动问题严重、水轮机空载工况不稳定和水泵高扬程区不稳定的根本原因；另外本项目还研究了环境因素对高水头水泵水轮机空化性能的影响，发现水轮机工况下，温度变化对空化性能的影响较大，在水泵工况下，温度降低使转轮内水流的湍动能增大，温度和大气压力降低使转轮叶片载荷降低，转轮空化性能下降。为了改善水泵水轮机的空化和振动性能，建立了转轮几何参数与性能参数之间的映射关系，并将可压缩流动的求解与转轮水力优化策略相结合，开发了考虑可压缩性的高水头水泵水轮机转轮设计与优化程序，寻求合理的高低压边安放角及叶片表面负荷分配，解决了水轮机转轮设计与水泵转轮设计中的多重矛盾问题，达到了抽水与发电的平衡，设计出了综合性能较优的高水头水泵水轮机转轮。本项目的研究对于完善高水头大容量水泵水轮机的设计理论、改善水泵水轮机的空化性能和抽水蓄能电站的运行稳定性，提高能源利用率具有重要的意义。